IDirectMusicSynth::PlayBuffer method (dmusics.h)

Artikel
12/05/2018

The PlayBuffer method downloads a stream of MIDI messages to the synthesizer.

Syntax

HRESULT PlayBuffer(
  REFERENCE_TIME rt,
  LPBYTE         pbBuffer,
  DWORD          cbBuffer
);

Parameters

rt

Specifies the start time of the buffer. This value is specified in REFERENCE_TIME units, relative to the master clock, which was previously set with a call to IDirectMusicSynth::SetMasterClock. Also, this value should be after the time returned by the clock in IDirectMusicSynth::GetLatencyClock.

pbBuffer

Pointer to a memory buffer containing the time-stamped MIDI messages that the IDirectMusicBuffer object generates

cbBuffer

Specifies the size of the buffer in bytes.

Return value

PlayBuffer returns S_OK if the call was successful. Otherwise, the method returns an appropriate error code. The following table shows some of the possible return status codes.

Return code	Description
E_POINTER	Indicates a bad buffer pointer.
DMUS_E_SYNTHNOTCONFIGURED	Indicates that the synth is not open or not properly configured.
DMUS_E_NOSYNTHSINK	Indicates that the IDirectMusicSynthSink object was not connected.
DMUS_E_SYNTHINACTIVE	Indicates that the method was called when the synth is inactive, which is not valid.
E_FAIL	Indicates that the method is unable to queue the messages.

Remarks

This is the software synthesizer's implementation of the IDirectMusicPort::PlayBuffer method. For details on the buffer format, see the description of IDirectMusicPort::PlayBuffer in the Microsoft Windows SDK documentation.

In order to properly associate the time stamp of each MIDI message in the buffer, the synth needs to convert from the REFERENCE_TIME format to its internal sample-based time. Because the wave-output stream is actually managed by IDirectMusicSynthSink, the synth calls IDirectMusicSynthSink::RefTimeToSample for each MIDI message to convert its time stamp into sample time.

Typically, the synthesizer pulls each MIDI message from the buffer, stamps it in sample time, and places it in its own internal queue. The queue is emptied later by the rendering process, which is managed by IDirectMusicPort::Render and called by the IDirectMusicSynthSink object.

For more information, see the descriptions of the IDirectMusic, IDirectMusicPort, and IDirectMusicBuffer interfaces in the Windows SDK documentation.

Requirements

Requirement	Value
Target Platform	Desktop
Header	dmusics.h (include Dmusics.h)

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